1. Field of the Invention
The present invention relates to an insulating-type switching electric power source device having a DC-DC converter.
2. Description of the Related Art
FIG. 11 illustrates an example of an insulating-type switching electric power source device. The circuit shown in FIG. 11 is disclosed in Japanese Unexamined Patent Application Publication No. 5-153775, and defines an insulating-type fly-back converter. This fly-back converter has a transformer 1, with a switch device Q being provided at the primary side (primary coil 2 side) of the transformer 1, and a secondary-side rectification smoothing circuit 4 being provided at the secondary side (secondary coil 3 side) of the transformer 1.
At the fly-back converter, input voltage Vin at the primary side is subjected to voltage conversion based on the switching operation of the switch device Q, and voltage induced by the secondary coil 3 of the transformer 1 is subjected to rectification smoothing by the secondary-side rectification smoothing circuit 4 and is supplied to a load 5. The ratio between the voltage Vout output to the load 5 and the input voltage Vin to the primary side (i.e., the input/output conversion ratio) can be carried by controlling the time ratio of the switch device Q. Accordingly, a configuration is provided for controlling the time ratio of the switch device Q, so as to stabilize the output voltage Vout to the load 5. That is to say, an auxiliary coil 6, primary-side rectification smoothing circuit 7, control circuit 8, and load regulation correcting circuit 9, are disposed at the primary side of the transformer 1.
The primary-side rectification smoothing circuit 7 is connected to the auxiliary coil 6, for performing rectification smoothing of the voltage inducted by the auxiliary coil 6, and has a circuit configuration which is approximately the same as that of the secondary-side rectification smoothing circuit 4. The voltage Vest which has been subjected to rectification smoothing by the primary-side rectification smoothing circuit 7 corresponds to the output voltage Vout.
The control circuit 8 uses the rectification smoothing voltage Vest by the primary-side rectification smoothing circuit 7 as detection signals of the output voltage Vout (i.e., output voltage detection signals), and controls the time ratio of the switch device Q so as to stabilize the output voltage Vout. That is to say, indirect control for indirectly stabilizing the output voltage Vout is performed by controlling the voltage wherein the output of the coil 6 provided to the primary side of the transformer 1 has been subjected to rectification smoothing.
The output voltage Vout fluctuates due to fluctuation in the current flowing through the secondary side circuits (i.e., the secondary coil 3 or secondary-side rectification smoothing circuit 4), but the fluctuation of the output voltage Vout due to the current fluctuation at the secondary side (i.e., output current fluctuation) is not manifested in the rectification smoothing voltage Vest of the primary-side rectification smoothing circuit 7. Accordingly, in the event that the rectification smoothed voltage Vest is used as output voltage detecting signals without change to perform switching control of the switch device Q, there is no compensation made for the fluctuations of the output voltage Vout due to the fluctuations in output current. Accordingly, the load regulation correcting circuit 9 is provided in the example, in order to compensate for the fluctuations in the output voltage Vout due to the output current fluctuations.
This load regulation correcting circuit 9 includes a resistor 10 and a load regulation correcting signal creating unit 11. A portion is provided on the primary side for conducting a current correlated with the output current, and the resistor 10 is introduced in such a portion. Accordingly, voltage correlated with the output current is generated at this resistor 10.
The load regulation correcting signal creating unit 11 creates load regulation correcting signals based on the voltage of the resistor 10. The load regulation correcting signals correspond to the output current, and are applied to the output voltage detecting signals Vest output from the primary-side rectification smoothing circuit 7. Accordingly, the output voltage detecting signals Vest are corrected according to fluctuations of the output voltage Vout due to output current fluctuations.
The control circuit 8 performs time ratio control for the switch device Q using the corrected output voltage detecting signals Vest, and accordingly can also compensate for fluctuations in the output voltage Vout due to output current fluctuations, thereby increasing output voltage precision.
Now, the resistance values of the secondary coil 3 of the transformer 1 and the resistance values of the lines of the circuit at the secondary side and so forth fluctuate according to fluctuations in the ambient temperature. Accordingly, even in the event that the flow of the current being conducted through the secondary side circuit is the same, the amount of voltage drop at the secondary side circuit changes due to fluctuations in the ambient temperature. Accordingly, load regulation properties such as indicated by the solid line A in FIG. 3A under a low temperature environment change so the inclination of the load regulation properties are such as indicated by the dotted line B in FIG. 3B under a high temperature environment, and the output voltage Vout also changes.
However, with the circuit configuration shown in FIG. 11, the load regulation correction amount by the load regulation correcting circuit 9 does not change according to the ambient temperature. Accordingly, fluctuations in the load regulation properties due to fluctuations in the ambient temperature cannot be compensated for, leading to problems such as deterioration in output voltage precision and so forth. Further, the inclination of the load regulation properties is greater under high temperature environments, and is smaller under low temperature environments, so there has been a problem in that current balance cannot be maintained under parallel operations.
In order to overcome the problems described above, preferred embodiments of the present invention provide an insulating-type switching electric power source device wherein compensation can be made for fluctuations in load regulation due to fluctuations in ambient temperature, output voltage precision is excellent, and current balance is readily achieved in parallel operations at all times, regardless of the fluctuations in the ambient temperature.
To this end, an insulating-type switching electric power source device according to a preferred embodiment of the present invention includes a transformer having a primary side and a secondary side, a switch device provided at the primary side of the transformer, converting input voltage of the primary side of the transformer to output voltage of the secondary side of the transformer, a primary side rectification smoothing circuit provided at the primary side of the transformer, performing rectification smoothing of the voltage of a coil of the transformer, a control circuit for using the voltage subjected to rectification smoothing as detection signals of output voltage, and controlling the time ratio of the switch device so as to stabilize the output voltage, a load regulation correcting circuit detecting current correlated with output current by a current detecting device provided in a circuit at the primary side, generating load regulation correcting signals having a correlation with output current from the detected current, and correcting detection signals of the output voltage, according to output voltage fluctuations due to output current fluctuations, and a temperature compensating circuit for changing the amount of load regulation correction by the load regulation correcting circuit according to the fluctuations in the ambient temperature, so as to reduce the amount of load regulation correction under low-temperature environments, and to increase the amount of load regulation correction under high-temperature environments.
With preferred embodiments of the present invention, the detecting signals of output voltage are corrected by load regulation correcting signals output from the load regulation correcting circuit, according to fluctuations in output voltage due to fluctuations in output current. Moreover, a temperature compensating circuit for the amount of load regulation correction is provided thereto, so the detecting signals of the output voltage are also corrected according to fluctuations in load regulation due to fluctuations in the ambient temperature.
Accordingly, the control circuit performs time ratio control for the switch device using detecting signals of output voltage following the correction, so the output voltage precision can be improved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.